Process for burning oily residues in tankers

ABSTRACT

A METHOD FOR DISPOSING OF LOW FLASH POINT CRUDE OIL RESIDUES RECOVERD FROM CARGO TANKS F SHIPS BY BLENDING THE LOW FLASH POINT RESIDUE WITH HIGH FLASH POINT FUEL OIL TO PROVIDE A BLENDED FUEL OF SUFFICIENTLY HIGH FLASH POINT FOR SAFELY BURNING ON BOARD SHIPS. THE BLENDED FUEL MAY THEN BE BURNED IN THE PROPULSION SYSTEM OF THE SHIP OR FOR STEAM GENERATION ON BOARD THE SHIP.

United States Patent Int. (:1. (2101 1/04 s. or. 44-80 6 Claims ABSTRACTOF THE DISCLOSURE A method for disposing of low flash point crude oilresidues recovered from cargo tanks of ships by blending the low flashpoint residue with high flash point fuel oil to provide a blended fuelof sufficiently high flash point [for safely burning on board ships. Theblended fuel may then be burned in the propulsion system of the ship orfor steam generation on board the ship.

This invention relates to a method fordisposing of lowflash point crudeoil residues remaining in cargo tanks of tankers or other ships afterthe bulk of the crude oil has been discharged therefrom.

'In recent years pollution of the seas by oil has become an increasinglyserious problem. One cause of pollution has been the practice of washingresidual crude oil from car-go tanks of tankers at sea and dischargingthe washings or slops overboard. In the operation of a tanker, it isnormally necessary to clean one or more of the cargo tanks on the returnvoyage to the loading port and refill these tanks with sea water asballast to enable the tanker to be safely handled during the dockingoperations. Afterwards the clean ballast water is pumped overboard tomake room for fresh cargo. For many years it was the practice of theindustry to pump the slops from such tank cleaning operations overboardin non-prohibited areas on the return trip to the loading port. However,even though carried out at a considerable distance from land, thedischarge of slops, especially slops resulting from washing of crude oilcargo tanks, may add to the pollution of the seas and the possiblekilling of marine, plant and bird life as well as damage to coasts andbeaches.

Previously, a method known as load on top has been proposed to restrictpollution due to the pumping of slops overboard. In accordance with thismethod, the slops are collected in one or more of the ships cargo tanks,commonly called slop tanks, and are permitted to settle to effectseparation into an oil phase floating on top of a water phase. The wateris then slowly withdrawn from the bottom of the tank and discharged tothe sea until oil is observed in the discharge. At this point, there isleft in the bottom of the slop tank, a small amount of free water on topof which is a layer of oily residue which contains some water emulsifiedtherewith. Fresh oil cargo is loaded on top of the retained oily residuewhen the vessel reaches the loading port and the layer of residue isdischarged at the discharge port together with the regular cargo.

The load on top system has a number of serious disadvantages, amongwhich is the fact that some refineries object to receiving cargocontaminated with the oily residues from tank washings. These residuesare generally of very poor quality as compared with crude oil and arecontaminated with large amounts of water and salts. The salt waterpresent in such residues will, if not removed at considerable expense,cause serious corrosion of metal in refinery units.

In the past, some consideration has been given to the possibility ofburning recovered slops as fuel for the propulsion system of ships. Suchdisposition of the slops has the obvious advantage of recovering fuelvalues as well as avoiding contamination of the seas. Unfortunately, therelatively low flash point of most crude oil and slops obtained bywashing crude oil cargo tanks has in the past made crude oil itself andrecovered slops unsafe for burning on board ship.

More recently, means have been found to burn crude oil and slops safelyon shipboard. For instance, US. Pat. 3,3 62,370 to Morrell describesapparatus which has been devised for safely burning low flash pointcrude oils and slops as fuel for the propulsion systems of tankers orother ships. While the Morrell system is highly advanta-geous wherelarge quantities of crude oil are to be burned, the use of such a systemdoes of course involve additional expense in the initial construction ormodification of tankers. Such expense is easily justified for shippingoperations in which it is anticipated crude oil will be available at alower price than bunker fuel but is diflicult to justify merely tohandle slops recovered by washing crude oil cargo tanks. A cheapermethod of disposing of such slops is highly desirable in suchsituations. Accordingly, it is an object of the present invention toprovide a method for safely burning such slops without the need forspecial equipment.

The present invention contemplates blending low flash point oily residueor slops recovered from washing crude oil cargo tanks with high flashpoint fuel oil to form a blended fuel of sufficiently high flash pointthat it can be safely burned in the propulsion system of ships or forgeneration of steam on board ships without the necessity for specialequipment or safety precautions, such as are needed for burning lowflash point material.

The American Bureau of Shipping specifies that fuels for ships must havea flash point not less than 120 F. unless special equipment such as thatdescribed in the above-mentioned Morrell patent is to be used to protectagainst the danger of explosions. The present invention is useful in theburning of residual crude oil having a flash point below 120 F.,preferably below 100F. and frequently in the range of to F.

The base fuel oil with which residual crude oil is blended in accordancewith the invention may be any suitable fuel oil having a flash point ofat least about F. Conventional bunker fuel oil frequently has flashpoints between about 170 and F. and is entirely satisfactory for thispurpose.

The blended fuel formed according to the present invention comprises abase fuel oil as described immediately above having a flash point of atleast 170 F. and may contain between about 1 and about 15 vol. percentresidual crude oil, preferably of the type described above and in anyevent having a flash point less than 120 F.. preferably less than 100 F.A preferred blended fuel is one containing between about and about vol.percent residual crude oil having a flash point between about 80 andabout 100 F. and between about 90 and 95 vol. percent base fuel oil suchas bunker fuel having a flash point between about 170 F. and about 180F.

Blended fuels of the present invention preferably contain no more thanabout lbs. of salt per thousand barrels of oil, no more than about 5volume percent (vol. percent) water, no more than about 0.1 weightpercent (wt. percent) sediment and less than about weight percent (wt.percent) wax. Excessive amounts of wax make it difficult to pump theresulting blended fuel while too much sediment tends to clog screens inthe fuel system. too much water tends to make burning dIfiICUlt andexcessive quantities of salt can cause excessive corrosion of lines andequipment.

Base fuel oil and the residual crude oil can be blended in any suitablemanner. Recovered residual crude oil can be accumulated in a tanksuitable for low flash point material. Suitable base fuel. such asconventional bunker fuel, can then be loaded on top. Ordinary loadingtechniques usually provide sufficient mixing to insure a proper blend ofthe two ingredients of the blended fuel. Alternatively, the base fueloil and residual crude oil may be mixed in any conventional mixingequipment and then stored for use as needed.

Residual crude oil may be recovered from empty crude oil cargo tanks inany suitable manner such as by the use of conventional tank washingtechniques followed by separation to remove excess water. A particularlyeffective technique for recovery of residual crude oil from cargo tanksof tankers is described in US. Pat. 3,364,893 to Edward G. Maddock.

The following examples will illustrate the practical application of thepresent invention to burning of a typical recovered residual crude oil(slop oil).

EXAMPLE I )omposltion Residual crudel Bunker p1 volume (volume Flashpoint percent) percent) F.)

EXAMPLE II Additional samples of the same recovered residual crude oildescribed above in Example I were blended with the Bunker C fuel havinga flash point of 172 F. to obtain alended fuels suitable for DUIl'lll'lgdirectly in the boilers 3f tankers or other ships as tollows:

While the invention has been described in connection with certainpreferred embodiments thereof, it will be understood by those skilled inthe art that various changes and modifications may be made withoutdeparting from the spirit and scope or the invention and it is intendedto cover all such changes and modifications in the appended claims.

We claim:

1. A method for safely burning residual crude oil having a flash pointless than 120 F. on board a ship which comprises mixing such residualcrude oil with a hydrocarbon fuel oil having a flash point above about170 F. to produce a blended fuel having a flash point above 120 F. andthen burning such blended fuel on board a ship.

2. The method of claim 1 in which the blended fuel comprises betweenabout 1 and about 15 vol. percent residual crude oil and between aboutand 99 vol. percent of the hydrocarbon fuel oil having a flash pointabove about 170 F.

3. The method of claim 2 in which the residual crude oil is residualcrude oil recovered from crude oil cargo tanks of a tanker and in whichthe blended fuel is used as fuel for the propulsion system of thetanker.

4. The process of claim 2 in which the flash point of the residual crudeoil is between about 80 and about 100 F. and in which the blended fuelconsists essentially of between 5 and about 10 ol. percent residualcrude oil and between about and about vol. percent fuel oil having aflash point above about F.

5. The method of claim 4 in which the hydrocarbon fuel oil has a flashpo1nt between about 170 and about i80 F.

6. The process of claim 5 in which the blended fuel contains less thanabout 20 lbs. of salt per thousand barrels of 011, less than about 5volume percent water, less than about 0.1 wt. percent sediment and lessthan about 40 wt. percent wax.

References Cited UNITED STATES PATENTS 7.362.370 l/l968 .VIorrell ll474.364.893 l/1968 Maddock 1l474 FOREIGN PATENTS l78.093 V1961 GreatBritain I08l5 OTHER REFERENCES Evans: Modern Petroleum Technology,London. The Tnstitute of Petroleum, 1962, pp. 614-615.

DANIEL E. WYMAN. Primary Examiner W. I. SHINE, Assistant Examiner Us.or. X.R, 114-14

